Heat-sensitive recording materials have been known for many years and have enjoyed a largely steady popularity. This may be explained in part by the fact that their use is associated with great advantages for merchants distributing tickets and/or sales receipts. Due to the fact that the color-forming components in the heat-sensitive recording process are contained in the recording material itself, it is possible to employ large numbers of thermal printers which operate without toner or ink cartridges and whose function need no longer be monitored by persons at regular intervals. Accordingly, this innovative technology has had extensive success particularly in public transportation and in the retail industry.
Increasingly over recent years, however, concerns have been voiced over the environmental soundness of certain color acceptors which, although they have no scientific basis whatsoever, cannot be ignored by industry, particularly commerce. Heat-sensitive recording materials containing                bisphenol A, i.e., 2,2-bis(4-hydroxyphenyl)propan and        bisphenol S, i.e., 4,4′-dihydroxydiphenyl sulfonehave been the focus of especial criticism which has primarily led to increased use of        Pergafast® 201, i.e., N-(p-toluenesulphonyl)-N′-3-(p-toluenesulphonyloxyphenyl)urea made by BASF Corporation, and        D8, i.e., 4-[(4-(1-methylethoxy)phenyl)sulfonyl]phenol.In considering this market situation which has changed completely within a very brief period of time, the inventor recognized the need for a novel color acceptor which, on the hand, is as completely biodegradable as possible and not harmful to the environment and which, on the other hand, must be at least economically practical, since ultimately even the best products must remain affordable and be affordable for the user.        